The prior art is replete with switches of various designs. For instance, the inventor herein joined in the conception and design of the devices taught by U.S. Pat. No. 3,368,049 entitled High Current Radio Frequency Switch, and U.S. Pat. No. 3,394,324 entitled Coaxial Switch. Both of these radio frequency devices, and many conventional switches have incorporated a vacuum envelope within which the contacts make and break a circuit through the switch. The inventor herein has pioneered vacuum-type radio frequency switches and other switches such as exemplified by the above noted patents and U.S. Pat. No. 3,261,953. The disadvantage inherent in a vacuum switch is that the cost of processing the vacuum switch tends to be prohibitive.
Additionally, because the atmosphere within the sealed vacuum envelope constitutes a high vacuum, it is especially difficult to achieve movement of parts relative to one another within the vacuum envelope without a certain amount of galling. The reason for such galling is that the surfaces of the metallic parts within a vacuum switch are so clean and free from oxidation that two metal parts that come together tend to stick together and resist relative movement one to the other. On the other hand, heretofor, it has not been practicable within the state of the art to produce a radio frequency switch that has the voltage standoff characteristics required for wide applicability without using a vacuum envelope. Accordingly, it is one of the principal objects of this invention to provide a switch structure which dispenses with the vacuum envelope.
Another of the disadvantages of conventional vacuum switches is the fact that these switches require the use of an external actuator to effect transfer or movement of the contact within the envelope. The use of external actuators has run the gamut from hydraulic to air, to solenoids, and to mechanical linkages adapted to effect transfer of the movable contact within the envelope. All such external actuators have required the utilization of a deformable vacuum tight wall in the nature of a flexible bellow or diaphragm interposed between the movable contact and the actuating mechanism. Where a solenoid has been used, it has been necessary to provide a vacuum tight seal between the coil structure of the solenoid and the armature thereof on which, or in association with which, is mounted the movable contact within the vacuum envelope portion of the switch. The use of such vacuum tight sealing methods and materials has required the utilization of special skills and fabrication techniques which contribute to the prohibitive cost of such devices. Accordingly, it is another object of this invention to provide a switch structure in which the contact element reciprocates and makes and breaks contact within a fluid medium.
So far as is known, a radio frequency switch has not been patented or successfully used in which the contact element of the switch constitutes a piston mounted for displacement between a switch "open" and switch "closed" position by the imposition of fluid pressure applied directly to the piston contact structure within the envelope, and which is useable for high direct or alternating current applications including radio frequency. Accordingly, it is a still further object of this invention to provide a switch structure suitable for both DC and radio frequency applications in which movement of the contact element is controlled by the direct application of fluid pressure thereto.
One of the problems that has been inherent in conventional vacuum switches has been the low contact pressure in such devices with attendant high contact resistance. Such low contact pressure derives from the fact that in all such switches contact pressure is dependent upon the external actuator which effects movement of the contact within the vacuum envelope. We have found, and it is therefore an object of this invention, that contact pressure be augmented several orders of magnitude, and result in decreased contact resistance, through design and fabrication of the fixed and movable contacts so that the contacts themselves, regardless of the actuating means therefor, generate or are responsible for the contact pressure and attendant low contact resistance.
Conventional radio frequency switches, both vacuum and air dielectric types, have been plagued by two obvious deficiencies. First, it is extremely important in a radio frequency switch that the inductance of the switch be kept to a minimum. Conventional radio frequency vacuum dielectric switches utilizing a bellow in the circuit in the conventional manner are subject to high inductance due to long current paths and are therefore limited in their application. Secondly, in conventional radio frequency switches little or no consideration is given to the distribution of voltage across the envelope, with the result that non-uniformly distributed high electrostatic stresses are imposed on the envelope, resulting in non-uniform heating of the envelope with attendant rupture thereof and destruction of the switch. It is therefor another object of the invention to produce an air-operated radio frequency switch which eliminates these deficiencies.
Still another object of the invention is the provision of a radio frequency switch capable of carrying high current in the order of 0 to 6000 amperes and which incorporates a contact assembly capable of handling DC or radio frequency signals up to about 50 megacycles.
The susceptibility of radio frequency switches to arcing between relatively movable members is well known. This is particularly true in a switch which is utilized in high current applications. One of the factors that initiates such arcing in a switch is contact "bounce" upon closing of the switch at high closing velocities. Accordingly, it is another object of the present invention to provide in a high current radio frequency switch a contact assembly and method of actuation thereof which inherently produces a built in resilience and resistance to contact bounce, thus reducing the tendency of the contact to generate an arc.
Among the factors that determine the cirtcuit breaking characteristics of a radio frequency switch is the efficiency with which heat generated in the contact elements is dissipated. It is well known that permitting the contact elements to operate at elevated temperatures increases the electrical resistance and thus lowers the current carrying capacity of the switch. This problem has been partially solved in the art by fabricating the relatively movable contact member of material possessing a large mass, the thought being that such large mass functions as a heat sink. This solution however introduces a new problem, namely, an increase in the inertial forces when the switch contact of large mass is moved at high velocity from one position to another. Such high inertial forces contribute to contact bounce and to arcing between the contact surfaces. Accordingly, it is yet another object of the present invention to provide a contact assembly for a high current radio frequency switch in which the contact assembly includes a piston moveable between requisite positions by the direct imposition of air pressure thereon, which also serves to absorb and convey away a large proportion of the heat from the radio frequency contact, and which works in conjunction with a fixed resilient contact that provides a multiplicity of short current carrying paths between the movable and fixed contacts.
In conventional radio frequency switches, whether they utilize a vacuum or an air dielectric, it has been unknown to use a single switch structure for different modes of operation. For instance, a single pole-single throw switch structure is not ordinarily also used for single pole-double throw or for cross-point applications. Accordingly, it is another object of the present invention to provide aa radio frequency switch structure which may be fabricated in either a single pole-single throw configuration, a single pole-double throw configuration, or double pole-double throw or even a multiplicity of poles interconnected to form a cross-point configuration.